/*
 * Copyright 2001-2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.logging;

/**
 * <p>
 * A simple logging interface abstracting logging APIs. In order to be
 * instantiated successfully by {@link LogFactory}, classes that implement this
 * interface must have a constructor that takes a single String parameter
 * representing the "name" of this Log.
 * </p>
 * 
 * <p>
 * The six logging levels used by <code>Log</code> are (in order):
 * <ol>
 * <li>trace (the least serious)</li>
 * <li>debug</li>
 * <li>info</li>
 * <li>warn</li>
 * <li>error</li>
 * <li>fatal (the most serious)</li>
 * </ol>
 * The mapping of these log levels to the concepts used by the underlying
 * logging system is implementation dependent. The implemention should ensure,
 * though, that this ordering behaves as expected.
 * </p>
 * 
 * <p>
 * Performance is often a logging concern. By examining the appropriate
 * property, a component can avoid expensive operations (producing information
 * to be logged).
 * </p>
 * 
 * <p>
 * For example, <code><pre>
 *    if (log.isDebugEnabled()) {
 *        ... do something expensive ...
 *        log.debug(theResult);
 *    }
 * </pre></code>
 * </p>
 * 
 * <p>
 * Configuration of the underlying logging system will generally be done
 * external to the Logging APIs, through whatever mechanism is supported by that
 * system.
 * </p>
 * 
 * @author <a href="mailto:sanders@apache.org">Scott Sanders</a>
 * @author Rod Waldhoff
 * @version $Id: Log.java 381838 2006-02-28 23:57:11Z skitching $
 */
public interface Log {

    // ----------------------------------------------------- Logging Properties

    /**
     * <p>
     * Is debug logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than debug.
     * </p>
     * 
     * @return true if debug is enabled in the underlying logger.
     */
    public boolean isDebugEnabled();

    /**
     * <p>
     * Is error logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than error.
     * </p>
     * 
     * @return true if error is enabled in the underlying logger.
     */
    public boolean isErrorEnabled();

    /**
     * <p>
     * Is fatal logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than fatal.
     * </p>
     * 
     * @return true if fatal is enabled in the underlying logger.
     */
    public boolean isFatalEnabled();

    /**
     * <p>
     * Is info logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than info.
     * </p>
     * 
     * @return true if info is enabled in the underlying logger.
     */
    public boolean isInfoEnabled();

    /**
     * <p>
     * Is trace logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than trace.
     * </p>
     * 
     * @return true if trace is enabled in the underlying logger.
     */
    public boolean isTraceEnabled();

    /**
     * <p>
     * Is warn logging currently enabled?
     * </p>
     * 
     * <p>
     * Call this method to prevent having to perform expensive operations (for
     * example, <code>String</code> concatenation) when the log level is more
     * than warn.
     * </p>
     * 
     * @return true if warn is enabled in the underlying logger.
     */
    public boolean isWarnEnabled();

    // -------------------------------------------------------- Logging Methods

    /**
     * <p>
     * Log a message with trace log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void trace(Object message);

    /**
     * <p>
     * Log an error with trace log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void trace(Object message, Throwable t);

    /**
     * <p>
     * Log a message with debug log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void debug(Object message);

    /**
     * <p>
     * Log an error with debug log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void debug(Object message, Throwable t);

    /**
     * <p>
     * Log a message with info log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void info(Object message);

    /**
     * <p>
     * Log an error with info log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void info(Object message, Throwable t);

    /**
     * <p>
     * Log a message with warn log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void warn(Object message);

    /**
     * <p>
     * Log an error with warn log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void warn(Object message, Throwable t);

    /**
     * <p>
     * Log a message with error log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void error(Object message);

    /**
     * <p>
     * Log an error with error log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void error(Object message, Throwable t);

    /**
     * <p>
     * Log a message with fatal log level.
     * </p>
     * 
     * @param message
     *            log this message
     */
    public void fatal(Object message);

    /**
     * <p>
     * Log an error with fatal log level.
     * </p>
     * 
     * @param message
     *            log this message
     * @param t
     *            log this cause
     */
    public void fatal(Object message, Throwable t);

}
